I don’t quite know what to do with that. I tried the solutions I found here in the forum, but to no avail.
Compared to others I’m a total newbie, so I’d appreciate a step-by-step solution, if there is any.

Hmm, what tells us that? Obviously the hardware and software requirements are met:
It’s a Raspi 2, with Raspbian Jessy installed, with all the software up to date.
The Unicorn Hat installation script has installed all the necessary software, hasn’t it? (see the output of pip list above)

So for the Unicorn python scripts it obviously makes no difference if the Hat is on or off, so maybe the error occurs because the Hat is not recognized at all. Because it’s broken?
I have no idea. Any more guesses?

I don’t think the HAT is the culprit, I do not get that error (or any error) running that script on a bare Pi. I tried with 3 different ones now, just to be sure, using a clean but updated Jessie.

I am not sure what the problem is, the main difference I can see between my tests and yours is that your Pi is obviously not the one I’m using. That’s not to say I think it’s defective, but it’s a possibility.

I think we need to summon the whiz @gadgetoid here to shed some light on the error itself… but from what I can tell the init can’t assess that PWM is working properly and I can reproduce the error if I target a pin other than 18.

Did this ever get resolved because I’m having the same problem and error code with the only difference being that my Raspberry Pi model is a B+ which I thought was more compatible with the Unicorn Hat anyway, but apparently not. I have tried your auto set-up command on multiple different images (fresh install) including the latest Raspbian Jessie, but to no luck I still get the same error message. I really don’t think my Raspberry Pi is broken as it is relatively unused, but maybe coincidentally me and bingobongo just got lucky with 2 broken models. My Unicorn Hat is brand new and came in the mail 2 weeks ago, but with multiple efforts to get it working I have had no luck. I would like if this issue could get re-looked at or at least get a status update and maybe get some comment from @gadgetoid if he hasn’t already starting looking in to it.

Garbled/intermittent display on Unicorn HAT/PHAT

On Raspbian 2016-05-10 / NOOBS 1.9.1 booting to X seems to do something with analog audio, where it would have otherwise been left alone and worked, mostly, by sheer luck. You need to force your Pi to HDMI audio using these lines in /boot/config.txt

hdmi_force_hotplug=1
hdmi_force_edid_audio=1

This pretends an HDMI monitor is plugged in, and that it supports audio.

You can also start in CLI mode, which doesn’t load whatever audio stuff is being used in X and has the same effect.

Failed with code -1

If you see something like ws2811_init failed with code -1 this is because you’re running an old version of the rpi-ws281x library on a Pi that it doesn’t recognize. This could be hardware version 0x13 which is a previously unsupported version of the Model B+ as far as I’m aware, or much more likely version 0x900093 which is the Raspberry Pi Zero v1.3 ( new model with camera port )